Hydraulic control device for automatic transmission

ABSTRACT

A hydraulic control device for an automatic transmission, having a gear ratio different from that of usual D range by a manual shift down from the D range to range 3 or 2, is mounted on an automobile. A first solenoid valve, a first shift valve and a second shift valve are connected so that the first solenoid valve controls the first and second shift valves. A second solenoid valve, a third shift valve and a down shift control valve are connected so that the second solenoid valve controls the third shift valve and the down shift control valve. Oil paths through which line pressure is applied in accordance with the range at which the manual valve is set are connected to certain shift valves, so that motions of the valves in the shift valves and the down shift control valve are constrained in accordance with the set range of the manual valve.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a hydraulic control device particularlydesigned for an automatic transmission of an automobile having amultiple speed transmission such as a five speed automatic transmission,and in detail relates to a hydraulic control device for setting gearratios which are different from those of a conventional automatic driverange during a "manual-shift-down" such as from Drive to 3rd, 2nd and1st range by a shift lever.

2. Description of the Prior Art

An automatic transmission, in general, performs a shift down operationthrough an ordinary gear ratio as well as manual shift down performed bya shift lever to reduce the speed of a vehicle on a long down slope andwhen passing other cars.

An applicant of the present invention, as shown in the Japanese Pat. No.57-37140, proposed an automatic transmission having a sub-transmissionmechanism (two forward speeds) and a main-transmission mechanism (threeforward speeds), with the transmission of both sub and main transmissionmechanisms operated by respective shift valves, which makes possible anautomatic transmission having six forward speeds. The thus proposedautomatic transmission has six forward speeds in the Drive range fromthe combination of sub and main transmission mechanisms, while on theother hand, the automatic transmission has three forward speeds in thecombined intermediate and low ranges when the submechanism is not used.

Accordingly, a conventional three or four forward speed automatictransmission only regulates shifting to a higher speed with an ordinarygear ratio and cannot select a suitable gear ratio for the runningcondition even though manual shift down is performed to obtain higheracceleration when passing other vehicles or applying the engine as abrake when a vehicle is running on a long down slope.

Furthermore, a multiple speed automatic transmission device having amain transmission mechanism and a sub transmission mechanism can havedifferent shifting patterns in the Drive range and the intermediate andlow ranges; however, in such an arrangement, three solenoid valves arerequired for first, second and third shift valves respectively.Incorporating expensive solenoid valves in the system causes the totalcost of the automatic transmission to increase.

OBJECT AND BRIEF SUMMARY OF THE INVENTION

It is the object of the present invention to provide a hydraulic controldevice capable of providing shifting pattens different from ordinaryshift patterns by manual shifting operations, but in which the number ofsolenoid valves is not increased beyond the number employed normally. Tothis end, there is provided a hydraulic control device which can beapplied, for example, to a five speed automatic transmission with fourselectable gear ranges D-3-2-1, and in which first and second solenoidvalves are provided to constrain first, second and third shift valvesand the down shift control valve in accordance with a certain range ofmovement of the manual valve. Because of the above arrangement, thestructure of the hydraulic control device is kept simple and does notrequire adding expensive solenoid valves. Furthermore, a multiple speedtransmission is provided which has different types of shift patternshaving gear ratios different from an ordinary automatic transmissionwhen manual shift down is performed. Because the hydraulic controldevice is simple and compact, in addition to having high fuelefficiency, suitable braking with the engine and suitable accelerationare obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a main portion of a hydrauliccontrol device in accordance with the present invention;

FIG. 2 is a schematic view of an automatic transmission mechanism towhich the control device of the present invention is applicable;

FIG. 3 is a diagrammatic view of a hydraulic control device applied to atransmission; and

FIG. 4 is an operation table showing the operation of the device of FIG.3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following is a description of an embodiment in accordance with thepresent invention.

A hydraulic control device according to the invention has hydraulicservos C for clutches, and hydraulic servos B for brakes which engage ordisengage certain components of a transmission gear mechanism; a firstshift valve 11, a second shift valve 12 and a third shift valve 13 whichcontrol oil supplied to each servo; and first solenoid valve S1, asecond solenoid valve S2 and a down shift control valve 15.

The first solenoid valve S1 controls the line pressure P_(L) to thefirst and second shift valves 11 and 12, and the second solenoid valveS2 controls the line pressure P_(L) to the third shift valve 13 and thedown shift control valve 15. At a certain position of a manual valve 10(for example, the position for 3 or 2 speed range), oil paths areconnected to certain shift valves and the down shift control valve toconstrain the motions of the shift valves and the down shift controlvalve corresponding to the positions of the manual valve 10.

With such a structure, when the manual valve 10 is positioned at the Drange, the first solenoid valve S1 controls the first shift valve 11 andthe second shift valve 12, and the second solenoid valve S2 controls thethird shift valve 13 and the down shift control valve 15. In accordancewith this motion of the valves, appropriate brakes and clutches areactuated and automatic transmission is performed.

When the manual valve 10 is positioned at the 3 range, line pressureP_(L) is applied to the port 3 as well as the port D, and the linepressure to the port 3 is applied through oil path 3a to the port 3b ofthe down shift control valve 15. The second solenoid valve S2 is shiftedto the off position so that the line pressure from the port D is appliedto the oil path Db, and the line pressure is applied to the rightcontrol oil chamber 13a of the third shift valve 13 and moves the spoolthereof; however, the line pressure of the oil path Db is also appliedto the right control oil chamber 15a of the down shift control valve 15which shifts the valve 15 to the left to an "upper half position" asshown in the upper half of the drawing, so that the line pressure of theport 3b is applied to the left control oil chamber 13b of the thirdshift valve 13 through the port 3c and the oil path 3d. The valve 13 iskept at a "lower half position" shown in the lower half of the drawingby a balance of a spring and the line pressure.

At this time, line pressure in the oil path La is applied through theport Lb, down shift control valve 15, port Lc and the oil path Ld to theleft control oil chamber 11b of the first shift valve 11; consequently,the valve 11 is held in the "lower half position". This means that thevalve 11 does not change its position no matter which condition (ON orOFF) the first solenoid valve S1 has, and only the second shift valve 12is controlled.

When the manual valve 10 is positioned at the 2 range, line pressure isapplied to the port 2 as well as the port D and port 3, the linepressure of the port 2 is applied through the oil path 2a and oil path2b to the left control oil chamber 12b, so that the valve 12 is held inthe "lower half position", and at the same time, line pressure runsthrough the oil path 2c to the left control oil chamber 15b of the downshift control valve 15. The valve 15 is thus held in the "lower halfposition".

A five speed automatic transmission 21 to which the hydraulic controldevice is applicable comprises a torque converter portion 22, a fourspeed automatic transmission mechanism portion 23 and an underdrivemechanism portion 25, as shown in FIG. 2.

The torque converter portion 22 has a torque converter 26 and a lock-upclutch 27. An engine crankshaft 28 is connected to an input shaft 29through oil flow in the torque converter 26 or through a mechanicalcoupling by the lock-up clutch 27.

The four speed automatic transmission mechanism portion 23 has a singleplanetary gear unit 30 and a dual planetary gear unit 31. Each gear unithas a carrier CR and a sun gear S. These carriers CR are connected toone another as an integrated body; and the sun gears are also connectedto one another as an integrated body. Still further, the input shaft 29is connected to the ring gear R₁ of the single planetary gear unit 30through the first (forward) clutch C₁ and also connected to the sun gearS through the second clutch C₂ ; and the sun gear S is restraineddirectly by the first brake B₁ and the rotation of the sun gear S in onedirection is regulated by the second brake B₂ through the first one-wayclutch F₁ ; and the ring gear R₂ of the dual planetary gear unit 31 isrestrained directly by the thrid brake B₃ and the rotation of the ringgear R₂ in one direction is regulated by the second one-way clutch F₂.Furthermore, the input shaft 29 is connected to the ring gear R₂ of thedual planetary gear 31 through the third clutch C₀ and the third one-wayclutch F₀ is arranged between the input shaft and the sun gear S inorder to regulate the rotation of the sun gear so that it does notexceed that of the input shaft 29. Further, the carrier CR is connectedto the counter drive gear 32 which is the output number of the fourspeed automatic transmission mechanism portion 23.

On the other hand, the underdrive mechanism portion 25 has a singleplanetary gear unit 33, a ring gear R₃ connected to a counterdriven gear35 always engaging with the counterdrive gear 32, and carrier CR₃ isconnected to the output pinion 36. Further, the rotation of the sun gearS₃ is regulated in one direction by the fourth one-way clutch F₃ ; andthe sun gear S₃ is restrained by the fourth brake B₄ and is connected tothe carrier CR₃ through the fourth clutch C₃.

As for the output pinion 36, it is connected to the right and left axes39r, 391 through the differential device 37.

The five speed automatic transmission 21 is controlled and operated by ahydraulic circuit 40 shown in FIG. 3.

In the hydraulic circuit 40, C₀, C₁, C₂ and C₃ are the hydraulic servosfor the clutches, and B₁, B₂, B₃ and B₄ are the hydraulic servos for thebrakes. 10 is the manual valve, the shift valve for shifting from range1 to 2 is the third shift valve 13, the shift valve for shifting fromrange 3 to 4 is the second shift valve 12, the fourth shift valve forshifting from range 4 to 5 is the shift valve 16, and 15 is the downshift control valve. S1 is the first solenoid valve to control the firstand second shift valves 11 and 12. S2 is the second solenoid valve tocontrol the third shift valve 13 and the down shift control valve 15. S3is the third solenoid valve to control the shift valve 16. 60 is alock-up control valve and S4 is the fourth solenoid valve to dutycontrol the lock-up control valve 60, and 61 is a lock-up modular valveto stabilize the duty control by the fourth solenoid valve S4. 63 is aprimary regulator valve, 65 is a secondary regulator valve, 66 is apressure release valve, 67 is a first modulator valve, 68 is a secondmodulator valve and 69 is a low modulator valve. 70 is a cooler, 71 is acooler by-pass valve and 72 is a throttle valve having a linear solenoidvalve to control line pressure up to a desirable level, 75 is anaccumulator control valve, 26 is the torque converter, 27 is the lock-upclutch, and P is a hydraulic pump. The first hydraulic servo for clutchC1, that of the second C2, that of the third C₀, and the secondhydraulic servo for brake B₂ are connected to a regulator valve 76,accumulator 77 and a check valve 79. An accumulator 80 (installationtype) is connected to the fourth brake hydraulic servo B4. In FIG. 3, asymbol like an electrical condenser in the line between lines 2b and 3ashows a separator plate to block the oil path so that the hydraulicdevice can be utilized for a valve body of a four speed automatictransmission.

An explanation will now be given of the operation of this embodiment.The five speed automatic transmission 21 provides a first to a fifthspeed in respective ranges (R, D, 3, 2 and 1) as set by the manual valve10. At each speed position of the manual valve, the first to the fourthsolenoid valves S1, S2, S3, and S4 in the hydraulic control circuit 40operate in accordance with the conditions shown in FIG. 4 and theclutches C₀ -C₃, the brakes B₁ -B₄, and the one-way clutches F₀ -F₃ areoperative or inoperative as shown in FIG. 4.

At the first speed in the range D, the first solenoid valve S1 is OFF(supply-condition), the second solenoid valve S2 is ON (drain-condition)and the third solenoid valve S3 is OFF (drain-condition). As shown inFIG. 1, the first shift valve 11 and the second shift valve 12 are inthe "upper half position", and the third shift valve 13, the fourthshift valve 16 and the down shift control valve 15 are in the "lowerhalf position". In this condition, line pressure from the port D ofmanual valve is applied to the first clutch hydraulic servo C₁ throughthe oil path Da, Dd, the port Dc, De of the fourth shift valve 16 andthe oil path Df. Line pressure P_(L), through the oil path Le is appliedto the fourth brake hydraulic servo B₄ through the port Lf, Lg of thethird shift valve 13 and the oil path Lh. By this motion in the circuit,the automatic transmission 21 engages the first forward clutch C1, andthe fourth brake B₄ operates. Then, the rotation of the input shaft 29is transmitted to the ring gear R1 of the single unit 30 through theclutch C1. At this time, the ring gear R₂ of the dual unit 31 isconstrained by the second one-way clutch F₂, and rotates the sun gear Swithout load in reverse; and the common carrier CR is rotated and muchretarded. The rotation is transmitted by the counter drive gear 32 tothe counter driven gear 35 of the under drive mechanism 25. The underdrive mechanism 25 is in "under drive condition" due to the operation ofthe fourth brake B₄ and the fourth one-way clutch F₃. Consequently, theautomatic transmission 21 as a whole operates in the first speed by thecombination of the first speed of the four speed automatic transmission23 and the under drive condition of the under drive mechanism 25.

At the second speed in the range D, the first solenoid valve S1 ischanged to ON (drain-condition). As shown in FIG. 1, the first shiftvalve 11 and the second valve 12 are in the "lower half position". Inthis condition, line pressure from the port D of the manual valve 10 isapplied to the second brake hydraulic servo B₂ through the oil path Dg,the port, Dh, Di of the shift valve 12 and the oil path Dj. By thismotion in the circuit, the first forward clutch C1 is engaged and thesecond brake B₂ is operated. Then, the rotation of sun gears isrestrained by the first one-way clutch F1. The rotation of the ring gearR₁ of the single unit 30 rotates the ring gear R₂ of the dual unit 31without load, and the carrier CR is rotated and retarded. The rotationis transmitted from the counter drive gear 32 to the counter driven gear35 of the under drive mechanism 25. The under drive mechanism 25 is in"under drive condition". Consequently, the automatic trasmission 21 as awhole operates in the second speed by the combination of the secondspeed of the four speed automatic trasmission 23 and the under drivecondition of the under drive mechanism 25.

At the third speed of the range D, the second solenoid valve S2 ischanged to OFF (supply-condition). The third shift valve 13 and the downshift control valve 15 are in the "upper half position". In thiscondition, line pressure from the oil path La is applied to the rightcontrol oil chamber 11b of the shift valve 11. Line pressure of the oilpath Le is applied to the fourth clutch hydraulic servo C₃ through portLf, Li of the shift valve 13 and the oil path Lj. In addition, thefourth brake hydraulic servo B₄ is released at the same time the fourthclutch C₃ is engaged, so that the under drive mechanism 25 is directlyconnected with the automatic transmission 23. Consequently, theautomatic transmission 21 as a whole operates at the third speed by thecombination of the second speed of the four speed automatic transmission23 and the direct coupling of the under drive mechanism 25.

At fourth speed in the range D, the first solenoid valve S1 is alsochanged to OFF (supply-condition). Line pressure is applied to the rightcontrol oil chamber 12a of the second shift valve 12. The second shiftvalve 12 is shifted to the "upper half position". Although line pressureis applied to the right control oil chamber 11a of the first shift valve11, the first shift valve 11 is kept at the "lower half position"because the chamber 11b is already pressurized and by the reaction forceof the spring. In this condition, line pressure from the port D of themanual valve 10 is applied to the third clutch hydraulic servo C₀through the oil path Dg, the port Dh, Di, the oil path Dj, the port Dk,Dl of the second shift valve 12, and the oil path Dm. By this motion inthe circuit, the first forward clutch C1 and the fourth clutch C3 areconnected, and the second brake B₂ operates and the third clutch C₀ isengaged. Then, the rotation of the input shaft 29 is transmitted to thering gear R1 of the single unit 30 through clutch C1. At this time, therotation of the input shaft 29 is transmitted to the ring gear R2 of thedual unit 31 through the clutch C₀, and the components of the planetarygear units 30 and 31 rotate together, and by the carrier CR the rotationof the input shaft 29 is transmitted to the counter drive gear 32 withthe same rotation speed. Consequently, the automatic transmission 21 asa whole operates in the fourth speed by the combination of the fourspeed automatic transmission 23 and the direct coupling condition of theunder drive mechanism 25.

At the fifth speed in the range D, the third solenoid valve S3 ischanged to ON (supply-condition), and the fourth shift valve 16 is inthe "upper half position". The first clutch hydraulic servo C₁ isdrained through the port De and the drain port. Line pressure is appliedto the first brake hydraulic servo B₁ through the oil path Da, the portDn, Dr and the oil path Do. By this motion in the circuit, the firstforward clutch C1 is released and the first brake B₁ operates. Then, therotation of input shaft 29 is transmitted to the ring gear R2 of thedual unit 31 through the clutch C₀. At this time, the sun gear S isrestrained. The input shaft 29 rotates the ring gear R1 of the singleunit rapidly without load, and such high speed rotation is transmittedto the counter drive gear 32 as an "over drive". Consequently, theautomatic trasmission 21 as a whole operates in the fifth speed by thecombination of the four speed automatic transmission 23 and directcoupling of the under drive mechanism 25.

At the idle condition in the range D, the first solenoid is OFF and thesecond and third solenoids are ON, and line pressure to the first clutchservo C₁ is reduced by the C₁ modulator valve 67 to the level just belowthat at which the clutch is connected and the first brake B1 operates.The load is released from input shaft 29, creeping is prevented and thefirst clutch C₁ is connected when the mode is changed to the firstspeed; because the first brake B₁ operates, backward motion of thevehicle on a slope is prevented.

When shifting from the N to the R range, when the vehicle speed is lessthan a certain level (less than 7 km/h) or 0 (zero) the first and thirdsolenoids are OFF and the second solenoid is ON; and clutch C2 isconnected and the third brake B₃ (first reverse) operates. The rotationof the input shaft 29 is transmitted to the sun gear S through theclutch C2. Under this condition, the input shaft 29 rotates the ringgear R1 of the single unit 30 and the carrier CR in the reversedirection because the ring gear R2 of the dual unit 31 is restrained bythe third brake B3. The reverse rotation of the carrier CR istransmitted to the under drive mechanism 25 which is in the drivecondition through the counter drive gear 32.

When shifting from the N to the R range when the vehicle speed is morethan a certain level (7 km/h), the solenoid valve S1 is ON, the firstshift valve 11 and the second shift valve 12 are shifted, and the thirdbrake B3 is released. By this motion, shifting to R range when a vehicleis moving at this speed is prevented.

When the manual valve 10 is shifted to the range 3 by the shift lever orswitch, line pressure is applied to the port 3 as well as to port D.

In range 3, the first and second speeds are the same as those in rangeD, but the third and fourth speeds have different gear ratios. At thethird speed in the range 3, the solenoid valves S1, S2 and S3 are allOFF. The solenoid S1 is in the "supply condition", line pressure isapplied to the right control oil chambers 11a and 12a of the first andsecond shift valves 11 and 12, and the second shift valve 12 is shiftedto "upper half position". However, the first shift valve 11 is kept atthe "lower half position" because the left control oil chamber 11b issupplied with line pressure by the motion of the down shift controlvalve 15 the same as in the third, fourth, and fifth speed in the rangeD. Consequently, line pressure from the port D is applied to the secondbrake servo B2 through the oil path Dg, the ports Dh, Di of the firstshift valve 11 and the oil path Dj; furthermore, line pressure of theoil path Dj is applied to the third clutch hydraulic servo C₀ throughthe ports Dk, Dl of the first shift valve 12 and the oil path Dm. On theother hand, the second solenoid valve S2 is in the "supply condition",and line pressure is applied to the right control oil chamber 15a and13a of the down shift control valve 15 and the third shift valve 13, sothat the down shift control valve is shifted to the "upper halfcondition". But the third shift valve 13 is kept at the "lower halfposition" by the combination of the line pressure from the port 3applied to the left control oil chamber 13b through the oil path 3a, theports 3b and 3c of the down shift control valve 15 and the oil path 3d,and the spring in said control oil chamber 13b. Line pressure in the oilpath Le is applied to the fourth brake hydraulic servo B4 through theports Lf, Lg and the oil path Lh the same as for the first and secondspeeds. In the automatic transmission 21, the first clutch C₁ and thethird clutch C₃ are connected, and the second brake B₂ and the fourthbrake B₄ operate. The four speed automatic transmission mechanism 23 isplaced in a direct coupling condition and the under drive mechanism 25is placed in the drive condition. Then the third speed of range 3 isobtained. This condition, in general, provides a larger gear ratio thanthat of the third speed of range D, the engine braking is more effectiveand acceleration becomes better.

At the fourth speed in the range 3, the third solenoid valve S3 isshifted to ON. The fourth shift valve 16 is changed to the "upper halfposition", and line pressure from the port D is applied to the firstbrake hydraulic servo B1 through the ports Dn, Dr and the oil path Do.Consequently, in the automatic transmission 21, the third clutch C₃ isconnected, and the first, second and fourth brakes B1, B2 and B4operate. Thus, the four speed automatic transmission mechanism 23 isplaced in the drive condition and the under drive mechanism 25 is in theunder drive condition. As a whole, the transmission operates at thefourth speed of range 3. This condition, in general, provides a largergear ratio than that of the fourth speed in the range D.

When the manual valve 10 is shifted to the position for range 2, linepressure at the port L is applied to port 2 as well as ports D and 3.

At the first speed of range 2, the solenoid valves S1, S2 and S3 are inthe same conditiion as for the first speed in ranges D and 3, linepressure from port 2 is applied to the port 2e of the fourth shift valve16 through the oil path 2a and 2d, and because the fourth shift valve 16remains in the "lower half position", line pressure is also applied tothe port 2h of the second shift valve 12 through the port 2f and the oilpath 2g. On the other hand, because line pressure from the port 2 isapplied to the left control oil chamber 12b of the second shift valve 12through the oil paths 2a and 2b, the second shift valve 12 remains inthe "lower half position" in spite of line pressure being applied to theright control oil chamber 12a due to the solenoid valve S1 being OFF.Accordingly, because the second shift valve 12 remains in "lower halfposition", line pressure at the port 2h is applied to the third brakehydraulic servo B3 through the port 2i, the oil path 2j, the port 2k and2l of the first shift valve 11, which is in the "upper half position",and the oil path 2m. At this time, line pressure applied to the thirdbrake hydraulic servo B3 is suitably adjusted by the low modulator valve69 located in the oil path 2g as shown in FIG. 3. Accordingly, at thefirst speed of range 2, the third brake B3 is applied in addition to theconditions for the first speed in range D. Due to this action, the gearratio is the same as the first speed in the range D; however, at thetime when the engine is used as a brake, this first speed in range 2still maintains first speed because of the ring gear R2 beingconstrained by the third brake B3, whereas in the range D, thetransmission is disconnected by the one-way clutch F2.

At the second speed of range 2, the solenoid valve S2 is changed to OFF,and line pressure is applied to the right control oil chamber 15a of thedown shift control valve 15 and the port 13a of the third shift valve13. Thus the third shift valve 13 is shifted to the "upper halfposition". On the other hand, as line pressure is applied to the leftcontrol oil chamber 15b of the down shift control valve 15 through theoil path 2a and 2c, the down shift control valve 15 remains in the"lower half position" due to the action of the spring. Accordingly,because the down shift control valve 15 remains in the "lower halfposition", line pressure in the oil path Le is applied to the fourthclutch hydraulic servo C3 through the port Lf, Li and the oil path Lj.Accordingly, the first and the fourth clutches C1 and C3 are connectedand the third brake B3 operates. Thus, the four speed automatictransmission mechanism 23 is placed in first speed and the under drivemechanism 25 is placed in a directly coupling condition; as a whole, thesecond speed of range 2 is obtained. In this condition, in general, thegear ratio is greater than for the second speed of range D and range 3.At this time, as in the case of the first speed, the operation of theengine as a brake is kept at second speed because the third brake B3operates. In range 2, it is possible to obtain second and third speedslike those in range D as shown in parentheses.

Furthermore, at range 1, the first speed is the same as the first speedin range 2. As shown in the parentheses, a second speed the same as thatof the second speed in range 2 and a third speed the same as the thirdspeed in range D can be obtained.

In the hydraulic circuit 40 described above, if the solenoid valves S1,S2 and S3 fail, the transmission is automatically shifted in each, i.e.to the fourth speed in range D, third speed in range 3, second speed inranges 2 and 1, and by operation of the manual valve 10 by hand, it ispossible to obtain a suitable driving condition.

The above embodiment has been explained for a five speed automatictransmission having a four speed automatic transmission mechanism and anunder drive mechanism. However, the present invention can be applied toa four speed automatic transmission having the three speed automatictransmission mechanism and an under or over drive mechanism, and toother multiple speed automatic transmissions, etc.

What is claimed is:
 1. In an automatic transmission of a vehicle havinga transmission gear mechanism through which power is transmitted in arespective one of power transmitting paths defined therethrough:frictional engaging means operatively connected to the transmission gearmechanism for selecting the power transmitting path through which poweris transmitted in the transmission gear mechanism; hydraulic servosoperatively connected to the frictional engaging means for operating orreleasing or for engaging or disengaging the frictional engaging means;first, second and third shift valves operatively hydraulically connectedto the respective hydraulic servos and a source of line pressure andwhich shift valves are normally resiliently held in a first position andare movable to a second position by application of line pressure theretoin opposition to the normal resiliently held position, and in whichrespective positions the line pressure is supplied toward the servos andthe supply of line pressure is interrupted during forward travelling ofthe vehicle to provide different speeds which can be output by thetransmission while the vehicle is travelling forward; and a manual valveoperatively hydraulically connected in the transmission between a sourceof line pressure and the shift valves and which manual valve is settableto a plurality of ranges of forward speed; a hydraulic control devicecomprising:a first solenoid valve operatively hydraulically connectedbetween the source of line pressure and said first and said second shiftvalves for controlling supply of hydraulic fluid to said first and saidsecond shift valves for use in controlling the positions thereof; a downshift control valve normally resiliently held in a first position andmovable to a second position by application of line pressure thereto inopposition to the normal resiliently held position; a second solenoidvalve operatively hydraulically connected between said manual valve andsaid third shift valve and said down shift control valve for controllingsupply of hydraulic fluid to said third shift valve and said down shiftcontrol valve for use in controlling the positions thereof; andhydraulic fluid passages between said manual valve and said down shiftcontrol valve and between said down shift control valve and said thirdshift valve for, when said manual valve is at one of the ranges, linepressure is applied to said third shift valve through said down shiftcontrol valve to hold said third shift valve at the first position whensaid third shift valve and said down shift valve are supplied only withhydraulic fluid through said second solenoid valve, whereby when saidmanual shift valve is at said one of said ranges, said third shift valveis held in said first position regardless ON condition or OFF conditionof said second solenoid valve.
 2. A hydraulic control device accordingto claim 1 wherein said one range of said manual valve is a third range.3. A hydraulic control device according to claim 1 wherein saidautomatic transmission mechanism is constituted by a main transmissionmechanism and a sub transmission mechanism, and said first and secondshift valves are connected for controlling hydraulic servos in said maintransmission mechanism and said third shift valve is connected forcontrolling hydraulic servos in said sub transmission mechanism.
 4. Ahydraulic control device according to claim 1 further comprising furtherhydraulic fluid passages between said down shift control valve and saidfirst and second shift valves for, when said manual valve is at said onerange, and said down shift control valve is kept at the one position,the supply of hydraulic fluid controlled by said first solenoid valvecontrols the position of said first shift valve and said second shiftvalve to hold them in respective second positions, and when said downshift control valve is changed to the second position, line pressure isapplied to said first shift valve through said down shift control valveto hold said first shift valve in a second position against the supplyof hydraulic fluid from said first solenoid valve.
 5. In an automatictransmission of a vehicle having a transmission gear mechanism throughwhich power is transmitted in a respective one of power transmittingpaths defined therethrough: frictional engaging means operativelyconnected to the transmission gear mechanism for selecting the powertransmitting path through which power is transmitted in the transmissiongear mechanism; hydraulic servos operatively connected to the frictionalengaging means for operating or releasing or for engaging or disengagingthe frictional engaging means; first, second and third shift valvesoperatively hydraulically connected to the respective hydraulic servosand a source of line pressure and which shift valves are normallyresiliently held in a first position and are movable to a secondpositoin by application of line pressure thereto in opposition to thenormal resiliently held position, and in which respective positions theline pressure is supplied toward the servos and the supply of linepressure is interrupted during forward travelling of the vehicle toprovide different speeds which can be output by the transmission whilethe vehicle is travelling forward; and a manual valve operativelyhydraulically connected in the transmission between a source of linepressure and the shift valves and which manual valve is settable to aplurality of ranges of forward speed; a hydraulic control devicecomprising:a first solenoid valve operatively hydraulically connectedbetween the source of line pressure and said first and said second shiftvalves for controlling supply of hydraulic fluid to said first and saidsecond shift valves for use in controlling the positions thereof; a downshift control valve; a second solenoid valve operatively hydraulicallyconnected between said manual valve and said third shift valve and saiddown shift control valve for controlling supply of hydraulic fluid tosaid third shift valve and said down shift control valve for use incontrolling the positions thereof; and hydraulic fluid passages betweensaid manual valve and said first, second and third shift valves andbetween said manual valve and said down shift control valve for, whensaid manual valve is at one of the ranges, said oil passages areconnected to said shift valves and said down shift control valve foractuating the appropriate hydraulic servos corresponding to said onerange, and for, when said manual valve is changed to another of theranges, line pressure is applied to said second shift valve and to saiddown shift control valve in the same direction at the normal resilientholding of said second shift valve and said down shift valve for causingsaid second shift valve and said down shift control valve to be held inthe first positions thereof regardless of the ON condition or OFFcondition of said first and second solenoid valves.
 6. A hydrauliccontrol device as claimed in claim 5 wherein said one range of saidmanual valve is a second range.
 7. A hydraulic control device accordingto claim 5 wherein said automatic transmission mechanism is constitutedby a main transmission mechanism and a sub transmission mechanism, andsaid first and second shift valves are connected for controllinghydraulic servos in said main transmission mechanism and said thirdshift valve is connected for controlling hydraulic servos in said subtransmission mechanism.
 8. A hydraulic control device as claimed inclaim 5 in which when said manual valve is at said another of saidranges, only said second shift valve is held against movement to thesecond position.